This invention relates in general to thrust reversers for fan jet aircraft engines and, more specifically, to thrust reverses using a plurality of deployable door assemblies mounted in an engine nacelle.
Modern aircraft fan jet engines have a nacelle or shroud surrounding the engine, spaced outwardly from the core engine cowl to define an annular passage or duct for flow of air rearwardly from the outer portion of an enlarged axial flow compressor. In this type of engine, a large proportion of the total thrust is developed by the reaction to the air driven rearward by the fan and the balance results from ejection of the exhaust gas stream from the engine.
Aircraft using engines of this type tend to have high landing speeds, placing great stress on wheel braking systems and requiring very long runways. To reduce this braking requirement and permit use of shorter runways, means are now provided in such engines for reversing at least a major portion of engine thrust during the landing roll. Many different types of thrust reversers have been designed, of varying effectiveness.
One type, primarily used with non-fan type turbine engines, uses large, sturdy clam-shell like blocker doors which swing directly behind the jet exit nozzle and diverge forwardly to reverse thrust. This system must be very heavy and strong and is not easily applied to fan jet engines.
Another type of thrust reverser uses cascade sets in the sidewalls of the engine nacelle with devices for uncovering the cascades and blocking air flow through the annulus aft of the cascades to direct air flow through the cascades, which turn the airflow in a reverse direction. Typical cascade type thrust reversers include those disclosed by Jurich in U.S. Pat. No. 4,807,434, Montgomery in U.S. Pat. No. 4,145,877 and Hom et al in U.S. Pat. No. 3,500,646. While often effective, these systems are mechanically complex, requiring a great many cooperating components.
Still another design uses pivotable doors lying in openings in the sidewall of the shroud or nacelle which pivot outwardly while a second set of doors pivot inwardly to block flow of air through the duct and direct it to the outwardly extending doors which direct air flow rearwardly. Typical of these is the system disclosed by Ellis in U.S. Pat. No. 3,612,401. This system, while useful, tends to be heavy and mechanically complex using complex actuators to move the doors between stowed and deployed positions. Often portions of the door actuating mechanisms, hinges or the like, project into the engine air flow during normal operation and/or thrust reversal, reducing engine effectiveness.
Yet another design uses a plurality of pivotable doors located in openings arranged radially around the shroud. Each door pivots so that one end contacts the engine cowl blocking air flow through the annular duct while the other end extends outside the nacelle in a direction directing airflow forwardly. Typical of these are the systems disclosed by Maison et al in U.S. Pat. No. 3,605,411 and Helmintoller in U.S. Pat. No. 3,279,182. While having greater mechanical simplicity than other systems, it is difficult with this arrangement to provide optimum duct air flow blocking and optimum flow re-direction in the reverse direction. Powerful and heavy actuators are often needed because of the greater forces exerted on the large, single doors.
Thus, there is a continuing need for improved thrust reversing systems for use in ducted fan jet engines which combine highly effective flow reversal with low cost, light weight, mechanical simplicity, ease of maintenance and avoidance of interference with air flow both during normal engine operations and during thrust reversal.